Orthopaedic arthroplasty procedures often involve the use of an implant or implants which is used to replace an articulating surface or surfaces of the joint. Usually such implants are attached to a resected or otherwise prepared part of a patient's bone. A cutting guide can be attached to the patient's bone to allow surfaces of the bone to be resected to accept the implant. A variety of approaches are available to planning, guiding and placing the cutting guides, implants and other instruments used during the procedure, so as to try and ensure that the joint is correctly rebuilt. However, for some joints, such as the knee joint, it is also necessary to take into account the soft tissue structures of the joint, such as the ligaments, so as to try and ensure that the joint is correctly rebuilt.
Computer Assisted Surgery (CAS) systems can be used to plan and navigate the position of cutting guides, implants, etc in order to try and take into account soft tissue structures. The planned position of a cutting guide can be updated intra-operatively based on measurements of the soft tissues in order to adjust the cuts to be made to the bone to change the eventual position of the implant. However, CAS systems are expensive and are not widely available. Further some surgeons prefer not to use CAS systems and prefer to use their own workflow and techniques.
A non-navigated approach to positioning a cutting guide can be achieved by producing a patient specific cutting guide using data from captured images of a patient's bone (sometimes referred to as “templating”) so that the cutting guide can be attached in a predefined position to the patient's bone thereby fixing the position of the cuts in the planned position. However, this approach is not suitable for allowing soft tissues to be taken into account as the position of the cuts relative to the patient's bone is fixed pre-operatively. The actual cuts that may be required in order to take into account the soft tissue structures of the joint or for other reasons may only become apparent intra-operatively and so the cuts defined by the cutting guide are non-optimal.
The present invention provides a mechanism allowing intra-operatively available soft tissue information, or other information, to be used to make the correct cuts, without requiring a complex planning or navigation system.